Brasacanthus sphoeroidesgen. n.. sp. n. is described from the marine fish, Sphoeroides greeleyi (Steindachner), taken in Paranaguá Bay, Paraná State, Brazil. The new genus differs from Acanthocephalus Koelreuter, 1771, the nearest genus in the family Echinorhynchidae, by having very flat and variable lemnisci in both sexes and a uterine egg reservoir in the female. The species is characterized by its spherical body form and in having parallel or diagonal testes.